The European Fruit Lecanium Scale (Rhyacionia bouliana) is a soft scale that causes damage primarily on shade trees and other woody ornamental plants. The European Fruit Lecanium Scale Growing Degree Day Model can help to predict the timing of different life cycle stages.

European Fruit Lecanium Scale Life Cycle Stages

European Fruit Lecanium Scales overwinter as adults in twigs or branches, and adults emerge in late spring or early summer. Crawlers emerge later in summer and are active for a short time.

The periods of crawler emergence is key for insect prevention, if necessary. Researchers have created the European Fruit Lecanium Scale Emergence Growing Degree Day Model to better predict when the crawlers will emerge.

Calculating Growing Degree Day Units

The European Fruit Lecanium Scale Emergence Growing Degree Day model uses a lower threshold of 50F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

Using Jan. 1st as a default “biofix” date, or starting point for accumulation. Peak crawler emergence occurs approximately at  800 GDD(F). This can be used an approximate target for beginning treatments.

Source:

Kowalsick, Thomas, and Scott Clark. 2006. Using Growing Degree Days for Insect Pest Management. Cornell Cooperative Extension. 2006.